Exosomes are vesicles of endosomal origin that are secreted in the extracellular milieu following fusion of late endosomal multivesicular bodies with the plasma membrane (4). Cells from various tissue types have been shown to secrete exosomes, such as dendritic cells, B lymphocytes, tumor cells and mast cells, for instance. Exosomes from different origin exhibit discrete sets of proteins and lipid moieties (5,6). They notably contain proteins involved in antigen presentation and immuno-modulation suggesting that exosomes play a role in cell-cell communications leading to the modulation of immune responses. Indeed, exosomes from dendritic cells (DC) pulsed with peptides derived from tumor antigens elicit anti-tumor responses in animal model using the matching tumor (7,8). Methods of producing, purifying or using exosomes for therapeutic purposes or as research tools have been described for instance in WO99/03499, WO00/44389 and WO97/05900, incorporated therein by reference.
Considering their immunogenic and therapeutic properties, it would be particularly useful to be able to modify the content of exosomes in order to alter their properties. In this respect, recombinant exosomes have been described in the art, which derive from cells transfected with plasmids encoding recombinant proteins. Such recombinant exosomes contain the plasmid-encoded recombinant protein (WO00/28001).